Field of Invention
This invention relates to torque/speed transmissions, specifically to methods that can be used to “limit the maximum shaft rpm (speed) at which axial position changing of a variator mounted on it is performed to a “maximum axial position changing rpm value” for all variator mounted shafts of a CVT, while still allowing a safe driving experience and also allowing the driver to use the full power of the engine when needed. Examples of variators are: a cone with one torque transmitting member, a cone with two oppositely mounted torque transmitting members, a cone with two opposite teeth, a push belt pulley, etc. The methods of this invention are referred to as the “Maximum Axial Position Changing RPM Method”, the “Alternate Maximum Axial Position Changing RPM Method”, and the “Alternate Maximum Axial Position Changing RPM Method 2” and are described in the “Maximum Axial Position Changing RPM Method” section of this disclosure.
Description of Prior Art
A CVT that has the potential to replace automatic and manual transmissions in vehicles is a CVT 4, which is described in U.S. patent application Ser. Nos. 13/629,613, 13/730,958, and 13/889,049.
A CVT 4, which is shown in FIGS. 1 to 4, has one cone with one torque transmitting member mounted on one shaft/spline that is coupled to another cone with one torque transmitting member mounted on another shaft/spline by a transmission belt.
A CVT 4 is promising design because it can allow for the construction of non-friction dependent CVT's without using ratcheting or reciprocating mechanisms. However, if a CVT 4 is transmitting a large torque, then the tension in the transmission belt of the CVT 4 is also large. And sliding a transmission belt under large tension from small diameter of its cone to a large diameter of its cone, as required for transmission ratio change, will also require a large force.
A CVT 6, which is described in U.S. patent application Ser. Nos. 14/182,306, 14/186,853, 14/475,492 and this disclosure, has two CVT 4's for which the transmission belt tension in one of the CVT 4's can be reduced. Reducing the transmission belt tension in the CVT 4 for which the axial position of a cone of a CVT 6 has to be changed can significantly: reduce the transmission ratio changing force needed, shock loads that occur during transmission ratio changing, and wear due to transmission ratio changing.
The axial position of a cone of a CVT 6 has to be changed within less than a full revolution of that cone. As such, the duration available for changing the axial position of a cone of a CVT 6 depends on the rotational speed (rpm) at which the cones of the CVT 6 are rotating. By limiting the “maximum rotating speed at which axial position changing of a cone is performed”, the duration available for changing the axial position of a cone can be increased; and this will reduce the transmission ratio changing force needed and shock loads that occur during transmission ratio changing.
For example, when the “maximum rotating speed at which axial position changing of a cone is performed”, rpm_max, is limited to a “maximum axial position changing rpm value” of 3000 rpm; then based on the calculations in the “Sample Calculations for Axial Position Changing” section below, the initial force needed to change the axial position of a cone, F_initial, is 40 lbs and the shock loads during axial position of a cone is h_dropping=0.38 cm.
When the “maximum rotating speed at which axial position changing of a cone is performed”, rpm_max, is not limited to a “maximum axial position changing rpm value”, then axial position changing of a cone can occur when the engine is operating at its maximum rpm. Most car engines have a maximum rpm of about 6000 rpm. From the calculations in the “Sample Calculations for Axial Position Changing” section below for rpm_max=6000 rpm, we get F_initial=162 lbs and h_dropping=1.5 cm.
From the sample calculations of the previous paragraph we can observe that by limiting the “maximum rotating speed at which axial position changing of a cone is performed” to 3000 rpm, the force needed to change the axial position of a cone can be limited to 40 lbs. Without limiting the “maximum rotating speed at which axial position changing of a cone is performed”, the maximum rpm of the engine, which we assume is 6000 rpm, will determine the force needed to change the axial position of a cone, which for 6000 rpm is 162 lbs, or more than 4 times larger than that for 3000 rpm. In addition, at 6000 rpm, the shock loads due to axial position changing of a cone will also be about 4 times larger than that for 3000 rpm.
Without limiting the “maximum rotating speed at which axial position changing of a cone is performed”, a CVT 6 can be unpractical for configurations where a cone rotates at high speed, such as 12000 rpm for example. A cone can rotate at 12000 rpm for a maximum engine rpm of 6000 rpm and a transmission ratio (output speed/input speed transmission ratio) of 2:1.
The idea of limiting the “maximum rotating speed at which axial position changing of a cone is performed” so as to increase the duration at which axial position changing of that cone has to be performed is not novel. But only limiting the “maximum rotating speed at which axial position changing of a cone is performed” without a control sequence/method, can allow for an unsafe driving experiences such as when the CVT is stuck in a low transmission ratio because the “maximum axial position changing rpm value” is exceeded; or can limit the power of an engine, such when the engine is only allowed to run up to 3000 rpm instead of 6000 rpm so as not to exceed the “maximum axial position changing rpm value”.
The “Maximum Axial Position Changing RPM Method”, the “Alternate Maximum Axial Position Changing RPM Method”, and the “Alternate Maximum Axial Position Changing RPM Method 2” of this disclosure will disclose a control sequence/method that will limit the “maximum rotating speed at which axial position changing of a cone is performed” while also providing a safe driving experience and also allowing the driver to use the full power of the engine when needed.